Changed the growth rate of string buffers

The growth rate of string buffers was reduced from 2 to 1.5 (3/2).
As string buffers start larger (256~1024 bytes), they don't need to
grow that fast. Moreover, a lower rate allows multiplicative growth up
to larger sizes (3/2 of the maximum). (After that, the growth becomes
linear, which is mostly useless.)
2 files changed